Touch pads and touch screens (collectively “touch surfaces”) are becoming increasingly popular as input devices for performing operations in a computer system because of their ease and versatility of operation as well as to their declining price. Touch surfaces allow a user to make selections and move a cursor by simply touching the surface of a pad or the display screen, with a finger, stylus, or the like. In general, the touch surface recognizes the touch and position of the touch and the computer system interprets the touch and thereafter performs an action based on the touch.
Touch pads are well-known and ubiquitous today in laptop computers, for example, as a means for moving a cursor on a display screen. Such touch pads typically include a touch-sensitive opaque panel which senses when an object (e.g., finger) is touching portions of the panel surface. Touch screens are also well known in the art. Various types of touch screens are described in applicant's co-pending patent application Ser. No. 10/840,862, entitled “Multipoint Touchscreen”, filed May 6, 2004, which is hereby incorporated by reference in its entirety. As noted therein, touch screens typically include a touch-sensitive panel, a controller and a software driver. The touch-sensitive panel is generally a clear panel with a touch sensitive surface. The touch-sensitive panel is positioned in front of a display screen so that the touch sensitive surface covers the viewable area of the display screen. The touch-sensitive panel registers touch events and sends these signals to the controller. The controller processes these signals and sends the data to the computer system. The software driver translates the touch events into computer events. There are several types of touch screen technologies including resistive, capacitive, infrared, surface acoustic wave, electromagnetic, near field imaging, etc. Each of these devices has advantages and disadvantages that are taken into account when designing or configuring a touch screen.
In conventional touch surface devices, sensing circuitry measures the dynamic output signals generated by the touch-sensitive panels. The output signal is a dynamic signal in that it changes between two or more states (e.g., a “touch” or “no touch” condition). In conventional sensing circuitry, there is typically a plurality of operational amplifiers that amplify the output signals. Additionally, the sensing circuitry typically include signal compensation and conditioning (e.g., mixing to remove noise) circuitry to improve the accuracy and dynamic range of the output signal. A more detailed discussion of such sensing circuitry is provided in co-pending and commonly owned application No. 11/650,043, entitled “Front-End Charge Compensation Method and System,” concurrently filed herewith, the entirety of which is incorporated by reference herein.
Additionally, in touch surface devices where the output signal is a charge waveform (e.g., an output signal from a capacitive touch surface), a relatively large feedback capacitor is typically connected between the output of each amplifier and the inverting input of each amplifier in order to accommodate relatively large charge amplitudes at the inverting input of the amplifier. The charge amplitudes should be sufficiently large to provide a sufficiently high signal-to-noise (S/N) ratio. The large feedback capacitors, however, consume a significant amount of integrated circuit (IC) chip “real estate” and hence, add significant costs and size requirements to the IC chips.
Thus, the sensing circuitry can impose significant cost and size requirements on the design of an application specific integrated circuit (ASIC), especially if the sensing circuitry must sense a large number of output signals simultaneously in parallel. For large touch surface devices having a large touch-sensitive panel that can generate a large number of output signals simultaneously (e.g., those having a large number of column sense electrodes), the ASIC can become quite large and expensive.
Additionally, it is desirable to provide an ASIC that can process the outputs of smaller touch surface devices, without under-utilizing the capacity of the ASIC. However, manufacturing multiple different ASICs for different sizes of touch surface devices also results in cost disadvantages from a manufacturing standpoint.
Therefore, there is a need for a method and system for receiving and processing the output signals for large touch surface devices without imposing unduly large cost and size requirements for the processing circuitry. Additionally, the processing circuitry should be able to accommodate smaller touch surface devices without under-utilizing its processing capacity, which would be inefficient from a cost and design perspective.